1. Field of the Invention
The present invention relates to an elastic wave duplexer including an elastic wave filter, such as a surface acoustic wave filter or a boundary elastic wave filter, and, in particular, to an elastic wave duplexer having including a transmission filter chip and a reception filter chip that are flip-chip bonded to a laminated board using a face-down technique.
2. Description of the Related Art
For mobile communication devices, such as cell phones, in order to reduce the size, the demand for a composite electronic component including a plurality of electronic components integrated therein is increasing. To meet such a demand, a duplexer including a transmission filter and a reception filter integrated therein has been commonly used. The transmission filter and the reception filter are connected to an antenna terminal. In addition, to reduce the size of the filters, surface acoustic wave filters using surface acoustic waves have been used for the reception filter and the transmission filter.
Japanese Unexamined Patent Application Publication No. 2003-249842 describes an example of a duplexer including such a surface acoustic wave filter.
FIG. 9 is a plan view schematically illustrating the circuit configuration of the surface acoustic wave duplexer described in Japanese Unexamined Patent Application Publication No. 2003-249842. A surface acoustic wave duplexer 501 includes an antenna terminal 502 connected to an antenna, a transmission terminal 503, a first reception terminal 504, and a second reception terminal 505. The reception terminals 504 and 505 are balanced output terminals. The reception terminals 504 and 505 of the surface acoustic wave duplexer 501 can provide a balanced output.
One end of a transmission filter 506 and one end of a reception filter 507 are connected to the antenna terminal 502. That is, the transmission filter 506 and the reception filter 507 are commonly connected to each other and are connected to the antenna terminal 502. A matching circuit 508 is connected between the antenna terminal 502 and the reception filter 507. The transmission filter 506 is a surface acoustic wave filter having a ladder type circuit configuration. The circuit configuration includes a plurality of series-arm resonators S1, S2, and S3 and a plurality of parallel-arm resonators P1 and P2.
The reception filter 507 includes an input end 509 connected to the antenna terminal 502 via the matching circuit 508. One end of a first longitudinally coupled resonator type surface acoustic wave filter unit 510 and one end of a second longitudinally coupled resonator type surface acoustic wave filter unit 511 are connected to the input end 509. A third longitudinally coupled resonator type surface acoustic wave filter unit 512 and a fourth longitudinally coupled resonator type surface acoustic wave filter unit 513 are connected downstream of the first longitudinally coupled resonator type surface acoustic wave filter unit 510 and the second longitudinally coupled resonator type surface acoustic wave filter unit 511, respectively. The first to fourth longitudinally coupled resonator type surface acoustic wave filter units 510 to 513 are 3-IDT longitudinally coupled resonator type surface acoustic wave filter devices. One end of an IDT located in the middle of the third longitudinally coupled resonator type surface acoustic wave filter unit 512 is connected to one end of an IDT located in the middle of the fourth longitudinally coupled resonator type surface acoustic wave filter unit 513 and is connected to the first reception terminal 504. The other ends of the middle IDTs are commonly connected to each other and are connected to the second reception terminal 505.
The first to fourth longitudinally coupled resonator type surface acoustic wave filter units 510 to 513 are configured so that the phase of a signal flowing from the input end 509 to the first reception terminal 504 is inverted with respect to the phase of a signal flowing from the input end 509 to the second reception terminal 505.
In order to produce the surface acoustic wave duplexer 501 having such a circuit configuration, surface acoustic wave filter chips that define the transmission filter 506 and the reception filter 507 are mounted on a laminated board and are connected to an electrode pattern disposed on the laminated board using bonding wires.
In addition, a phase matching pattern defining the matching circuit 508 is provided at a certain height in the laminated board. More specifically, as shown by a schematic plan sectional view shown in FIG. 10, a meandering phase matching circuit pattern 521 is provided at an intermediate height in a laminated board 520. One end of the phase matching circuit pattern 521 is connected to an input end of a reception filter disposed on the laminated board 520. The other end is connected to the antenna terminal.
FIG. 11 is a schematic plan view illustrating a surface acoustic wave filter chip mounted on a top surface of the laminated board illustrated in an embodiment described in Japanese Unexamined Patent Application Publication No. 2003-249842. As shown in FIG. 11, a surface acoustic wave filter chip 522 that defines a transmission filter and a reception filter is mounted on the laminated board 520. The surface acoustic wave filter chip 522 is electrically connected to an electrode land provided on the laminated board 520 by, for example, a bonding wire 523.
Recently, to reduce the size of a surface acoustic wave duplexer, a surface acoustic wave filter chip is flip-chip bonded onto a laminated board using a bump. Since a bonding wire is not used, a bonding operation can be efficiently performed. In addition, the size of the surface acoustic wave duplexer can be easily reduced.
Accordingly, in the surface acoustic wave duplexer described in Japanese Unexamined Patent Application Publication No. 2003-249842, when a transmission filter and a reception filter defined by surface acoustic wave filter chips are mounted using a flip-chip bonding technique, a bonding wire need not be used.
On the other hand, in the surface acoustic wave duplexer 501, the matching circuit 508 is disposed between the antenna terminal 502 and the reception filter 507 so as to provide impedance matching. In the surface acoustic wave duplexer 501, this matching circuit 508 is defined by the meandering phase matching circuit pattern 521, as shown in FIG. 10. However, the inductance of the matching circuit 508 is obtained from not only the inductance of the phase matching circuit pattern 521 but also from the inductance of the bonding wire.
Accordingly, in the surface acoustic wave duplexer 501 described in Japanese Unexamined Patent Application Publication No. 2003-249842, the inductance value of the meandering phase matching circuit pattern 521 included in the laminated board can be reduced.
In contrast, in the structure in which a reception filter and a transmission filter are mounted on a laminated board using a flip-chip bonding technique, a bonding wire is not used. Therefore, the inductance of a bonding wire cannot be used. As a result, a line pattern of the impedance matching circuit that provides a large inductance in a small area is required. To meet such a requirement, a coil-shaped line pattern may be used. A coil-shaped line pattern can provide a large inductance, as compared to a meandering line pattern.
However, when a coil-shaped line pattern is provided on a laminated board, electromagnetic coupling occurs between the coil-shaped line pattern and one of a transmission filter and a reception filter. Therefore, the isolation characteristics may be deteriorated. In particular, if electromagnetic coupling occurs between the coil-shaped line pattern and the transmission filter, the isolation characteristic is deteriorated.